Cornell box images

The Cornell box is the ubiquitous test scene for global illumination.
It was introduced at Cornell university in 1984 when they developed the
radiosity algorithm, and it has since become a standard test scene
for new global illumination algorithms. Often the Cornell box (which
is a physical model at Cornell) appears in many different variations,
and the same is the case below where I have rendered several different
versions using a variety of algorithms.

Spectral rendering of the Cornell box

This is a rendering of the Cornell box according to the data provided
by Cornell. The image was rendered using multi spectral Monte Carlo
ray tracing and converted to an sRGB image for display.

Cornell box replica

This is a replica of (one of) the cornell box model first used
at the graphics lab. at Cornell. It is a typical radiosity scene
with polygonal faces and diffuse materials. Here it is rendered
using photon mapping. Note how photon mapping correctly renders
the shadows where the boxes touches the floor. In mesh based
approaches (such as radiosity) the shadows often do not match
up with the corners of the box elements due to lack of precision
in the mesh.

Cornell box with glass sphere

The original Cornell box contains only diffuse materials. With photon
mapping it is easy to render any type of material, and in this box
scene the left cube has been replaced by a glass sphere, which
complicates the light transport in the scene a bit futher. In
particular the glass sphere creates a caustic on the floor by
focusing the light from the light source.

Cornell box with translucent box

Here the right box is translucent. Note how the light bleeds from the light
source bleeds down through the box. Also note how the box still captures the
indirect illumination in the scene as well as acts as a secondary source for
the other elements such as the ceiling and the wall. This image was rendered
for the paper "A Rapid Hierarchical
Rendering Technique for Translucent Materials".

Ray Tracing, Photon Mapping, and Global Illumination

Ray tracing1.5 seconds

+ soft shadows7 seconds

+ caustics12 seconds

+ global illumination15 seconds

Path tracing reference

Cornell box series showing the effect of simulating global illumination.
All the images have been rendered at 1024x768 with 4 samples per pixel
on a Dual P3 800MHz Linux-PC. The ray tracing version took 1.5 seconds,
The version with soft shadows took 7 seconds. Adding caustics increased
the rendering time to 10 seconds and 2 seconds of photon tracing.
The global illumination version took 12 seconds to render and 3 seconds
of photon tracing time. For this scene the global photon map has
200,000 photons and the caustics photon map has 50,000 photons.

Finally, the path tracing reference image on the right
took a long time to render. The important thing to notice is that it
looks the same as the version rendered using photon mapping.

Fractal box with two spheres

This is a "fractal" version of the box scene.
The walls have been replaced with displacement mapped surfaces
(generated using a fractal midpoint subdivision algorithm) and the
model contains a little more than 1.6 million elements.
It was rendered using 200000 photons in the global photon map
and 50000 in the caustics photon map.
The rendering time was 14 minutes on a Dual PII-400MHz Linux PC.

Fractal box with two fractal spheres

This image is an agressively displacement mapped cornell box. Both
the walls and the spheres have been displaced using a turbulence
function. This type of model would be very hard to render using
other methods than photon mapping.
The rendering time was 8 minutes on a Dual P3-800MHz Linux PC.

Another Cornell box series

Diffuse box

Glossy box

Glossy box (path tracing reference)

This is another variation of the Cornell box. The first two images have been
rendered using the photon map and the irradiance gradient caching technique
as described in the paper
"Global Illumination using Photon Maps".
The first image was rendered with 4 samples per pixel and the rendering time
is 9 min. on a 100MHz Pentium computer running Linux. The second image
has a glossy floor (using Ward's anisotropic reflection model).
The glosy box image was rendered with 16 samples per pixel and the rendering
time is 50 min. on a 100MHz Pentium computer running Linux.
The path tracing reference image of the glossy box was rendered using
1000 samples per pixel (note that is still has noise in it).